1. Field of the Invention
This invention relates generally to the field of computers and more particularly to supplying multiple voltage configurations for supporting different families of commercially available semiconductor devices.
2. Description of the Related Art
The Intel compatible processor family has been extended with the introduction of MMX (MultiMedia extensions) technology. The Intel Pentium processor with MMX technology extends the Intel Pentium family of microprocessors. It is both binary compatible and pin compatible with a large family of Intel processors including: Intel 8086/88, 80286, Intel 386 DX, Intel 386 SX, Intel 486 DX, Intel 486 SX and Intel 486 DX2 processors. When designing computers, and more specifically printed circuit boards to accommodate the Pentium with MMX technology compatible processors, there are a number of electrical differences from the "Classic" or Intel Pentium processors and the Pentium with MMX technology that a systems designer must address. The main electrical difference is the operating voltage. Usually, the faster Classic Pentium processors, i.e., the processors with speeds equal to and greater to 75 MHz of clock speeds, require only one operating voltage for both the processor core and the processor I/O pins. This voltage is designated as V.sub.CC. For Classic Pentium processors with speeds of 75 MHZ, 100 MHZ, 120 MHZ, 133 MHZ and 150 MHZ, V.sub.CC is equal to 3.3 VDC. For Classic Pentium processors with clock speeds of 166 MHZ and 200 MHZ. V.sub.CC is 3.5 VDC. This information can be found in the Intel Pentium Processor Data Sheets, available online URL at www.intel.com and available for download at ftp://download.intel.com/design/pentium/datashts/ in an Adobe Acrobat format. System designers wishing to accommodate the entire family of these available faster Classic Pentium processors can connect all the voltage supply pins together on a single power plane and adjust the voltage to the power plane according to the Classic processor speed. The 3.3 VDC Classic Pentium processors can operate at 3.5 VDC. Therefore, a system designer can specify a power supply with 3.5 VDC output and run the entire Classic Pentium family of processors. However, most AT PC power supplies provide +5 VDC, Ground, +12 VDC and -12 VDC, to provide 3.5 VDC, special power supplies are needed. An alternate method system designer can use to avoid the cost of special power supples with 3.5 VDC output is the use of a DC to DC converter. A DC to DC converter, mounted locally on the system board to convert the 5 VDC to the 3.3 VDC required for the Classic Pentium Processor.
Unlike any of its Classic Intel Pentium predecessors, the Intel Pentium processor with MMX technology requires two separate voltage inputs. One voltage input of 3.3 VDC for the processor I/O pins, called V.sub.CC2, and second voltage of 2.8 VDC for the processor core called V.sub.CC3. System designers wanting to accommodate all the faster Pentium Classic processors and also the Pentium processors with MMX technology processors in a single printed circuit board design, must supply the two voltage requirements. One method in which a system designer provides the two voltage requirements is through a local DC to DC converter. Using a 5 VDC to 2.8 VDC DC to DC converter and a combination of jumpers, system board designers can accommodate the family of pin compatible faster Classic Pentium and Pentium with MMX technology compatible processors. However, this approach is not without its shortcomings. One shortcoming is the need to manually select jumpers to supply the correct core operating voltage for a selected processor. Correctly selecting jumpers can be difficult, especially for system board designs that support a variety of processors. Accordingly, a need exists to overcome this short coming.
The use of other pin compatible Pentium processors such as the AMD K6 100 MHZ to 300 MHZ family of processors with MMX technology require a core operating voltage that is different from the Intel processors with MMX technology. The core operating voltage, V.sub.CC3 is 2.2 VDC. Many system designers want to accommodate the AMD K6 100 MHZ to 300 MHZ family of processors with MMX technology plus the faster Intel Classic Processors and the Intel Processors with MMX technology must now provide a third level of operating voltage on top of the two previously mentioned. The system designer is faced with having to provide additional local DC to DC convertors on the system board with additional replacement jumpers. Providing multiple pluggable DC to DC converters to accommodate many different processor types can be expensive. Many users are apt to select one processor type when initially installing a system and lose or misplace the additional hardware to accommodate other processor types. The requirement of additional hardware in many ways defeats the purpose of having a configurable system board once the board is installed if the additional on board hardware is misplaced or lost. Accordingly, a need exists for a configurable system board without the need for supplying a variety of pluggable on board DC to DC convertors to provide the desired processor core operating voltage.
Another shortcoming with using multiple pluggable regulators on the system board with some additional replacement jumpers is the complexity of plugging in jumpers to support the various operating core voltages for microprocessors. Therefore, a need exists to provide a method and apparatus to automatically select the core processor voltage based on the type of processor installed.